In recent years, light-emitting elements such as light-emitting diodes (LEDs) have been applied to lighting units, backlights for liquid crystal image devices, and traffic signals, with further improvements in luminescence intensity being sought. It is possible to increase the luminescence intensity of light-emitting elements by increasing the amount of current to be impressed. However, simultaneous with this, since the light-emitting element is accompanied by heat generation, it is necessary to dissipate the heat more efficiently. When heat dissipation is insufficient, the temperature of the light-emitting element becomes high when on, leading to a drop in luminous efficiency, and so the target luminescence intensity is not obtained. Also, in the case of using a light-emitting element over an extended period, when the heat dissipation is insufficient, since the light-emitting element continues to generate high heat over a long time, the reliability of the light-emitting element falls, thereby raising the possibility of problems such as non-lighting occurring.
Also, in order to protect the light-emitting element from the external environment such as external forces and humidity, it is generally packaged. Moreover, in order to efficiently radiate forward light that is emitted from the light-emitting element, a lighting unit is known in which cup machined portions are formed at predetermined positions in one of two metal substrates that are combined, with the light-emitting elements being mounted in the cup machined portions (for example, refer to patent documents 1 and 2).
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2001-332768
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2001-332769